I think it should work fine, but an email to Raymarine would be worthwhile. They are usually good at answering technical problems.
Interfacing should be easy just connect the wires for seatalk, fluxgate, drive unit and power. They are even colour coded.

I need to know if they are interchangeable ie can I directly replace the type 100 with the 300 or are there additional modifications required to make the system work ?

There are several computers that will work but you need the exact control head number so Raymarine can tell you which ones will work. The fluxgate and rudder controls are the same but you may find a core pack with those bundled either more available or the same price.

i have a type 300 autohelm unit,and the only difference with the type 100 is the output current to the drive unit ;ie the 300 supplies higher current as was designed for type 3(larger)motors.

on another note if you change to newer sg1,raymarine core unit,you will need to change the control head as well,and gyro,but the rudder transducer and drive unit are the same,the newer sg series,with a st 6002 control head have the auto learn function and stabilised gyro,making for less power comsuption and better course holding in following seas.

Contact Ray Marine to finds the most compatible computer for your control head. It's the control head that determines what course computer can be used. Anything more than a few years old is out of date well at least in terms of what you can actually get.

Thaks, I have ST 7000 and this control head control only 100/300 model. Seems that things are moving to new course computer and control head but it is here in Europe app 2500-3000 Euro and I woul like to avoid this scenario :-) . This is reason I am looking for used type 300.

I'm in somewhat the same position. A used course computer might be found but you won't find a new one. Your ST7000 can use many of the new ones and you can keep control head, drive and rudder feedback you have as well. If you have enough slack in the wires you can just drop it in place and recalibrate and go. Yes, the new course computers are priced as you suggest. Personally, I would not go to the trouble of installing a used one. They were not made that well for as old as they would be once you found it. The wave soldered boards were not well known for high quality. Mine is 20 years old and has an intermittent failure. We have it rigged to be somewhat stable but it can't be truely fixed. I'm in search now and have a lead on one. if you can find someone that really knows how to fix them it might be fixed. There were some basic things that went wrong with the boards but there is no Ray Marineservice that will fix anything at the board level any more. I know the guy that trained evryone in this part of the world and his health is failing these days.

You may find a better price on a core pack instead of the bare computer since they may be stocked more often and you might snag a deal. By the end of the season you won't find one. The rudder feebacks are cheap and the fluxgate is not really expensive either. A spare rudder feedback is a good thing to have as they go bad too.

A good ST7000 can steer the boat in situations you could never sustain. I depend on mine a lot when the weather kicks up.

Dear Pblais
Yes it is Harlem`s dilemma. If you buy used you will regret if not you will regret too. From the other side I can buy some new X30+control head and all installed items on boat are compatible. It would be simpliest and maybe most clever. BUT, new one x30+control head (ST 7000 do not support X30) coast in UK EBay app 1600 US$+700 US$ control head in total 2300 US$ +250 US$ DHL shipping + 25% custom clearance included VAT. so in total 3200 US$. From the other side if found used type 300 it will be in total app 500 US$ in total I am in saddle. As you can see huge dilemma!
I am experienced engineer now retired (I have 57 years, but retired because I worked with beneficiary time). I worked like chief engineer for maintaining Motorola radio systems on component level. Of course I already open computer and found (for that time advance design, Philips Microcontroller series 80XX +ROM+some semiconductors as well as 2 pcs of IC 74hc4051D (smd version). tracking input I found that fluxgate input lines finished on one of those two IC`s. I found new IC`s but minded my age and fact I am not equipped with soldering iron for smd I am now in process to find who can do it for me. Would be nice to have and schematic diagram but c`est la vie. One of my old professor in college said once when we (pupils) ask schematic diagram to repair his TV he said " Why do you need SD it is not defect in diagram already in TV" "-).
So I will try to find one old but to try to repair old one. If I success I will inform you. From the other side one guy advice me to place NMEAcompass , it is not bad idea too minded all other function on 300 except flux gate compass work fine.
BR Dusko Jankovic